Involvement of pertussis toxin-sensitive GTP-binding proteins in sphingosine 1-phosphate-induced activation of phospholipase C-Ca2+ system in HL60 leukemia cells

Exogenous sphingosine 1-phosphate (S1P) induced Ca2+ mobilization, in association with an increase in inositol polyphosphate production reflecting activation of phospholipase C in HL60 leukemia cells. The increase in intracellular Ca2+ concentration ([Ca2+](i)) induced by S1P was inhibited by an appropriate treatment of the cells with pertussis toxin (PTX), U73122 (a phospholipase C inhibitor) or phorbol 12-myristate 13-acetate (PMA). In parallel with the Ca2+ response, these agents also inhibited inositol polyphosphate production. The SIP-induced Ca2+ response was also attenuated in the dibutyryl cAMP-induced differentiated cells, where GTP-binding protein-induced Ca2+ response is suggested to be enhanced, Lysophosphatidic acid (LPA) also increased [Ca2+](i) in the cells, but the maximal response was about half of that of S1P, and furthermore PTX and dibutyryl cAMP treatment hardly affected the LPA-induced Ca2+ mobilization. We conclude that exogenous S1P mobilizes Ca2+ through phospholipase C activation. The S1P-induced enzy me activation is at least partly mediated by PTX-sensitive GTP-binding protein-coupled receptors which may be different from LPA receptors.